1. Field of the Invention
This invention relates to multi-tier client-server applications, and, in particular, to the performance thereof. Specifically, this invention deals with the operating characteristics of an application based on the performance and availability of the resources and services required by the application.
2. Description of the Related Art
A typical application of the type contemplated by this invention is one that requires multiple resources (hardware and software) from multiple computers, for example, multiple user interfaces utilizing databases, a web application server, another web site, or a mainframe system, and a means for these resources to be connected. Performance of such an application can be degraded at any point for any reason, including scarcity or resources, overloading, etc.
This invention applies to any such multi-tier client-server application. In many cases, the components comprising a multi-tier client server application may be obtained from different software vendors, and have different methods for managing and monitoring their performance and availability.
Typically, such applications implement a multiplicity of business functions, with the implementation of each function being spread out across the various components in the system. For example, an equities trading application might contain business functions for quotes, trading, portfolio management and so on. FIG. 1 shows this example application. A user invocation of one of these functions could result in a chain of messages being sent across various components of the system. As a result, a problem in one of the components may generate symptoms in a number of other components of the system (due to missing or incorrect messages). Typically, the error message eventually seen by the user or system administrator bears little or no relation to the underlying problem. In addition, a problem with one component or resource that is used for one particular business function may result in errors or bottlenecks in other components of the system, which in turn cause failures in other business functions.
As an example, in the system shown in FIG. 2, a Java servlet that implements a user interface to a trade function accessing an Enterprise JavaBean (EJB) running in a web application server. The code that implements the Trade servlet checks the return status each time the Trade EJB is called, and if there has been a failure, it returns an error message to the user. This servlet will be accessed concurrently by many users, and if the function of the Trade Enterprise JavaBean is impaired, there will be a large number of Trade servlets with calls to Trade EJBs waiting for an error to be returned, and in the mean time tying up valuable resources on in the web server. Users attempting to access the Trade function may see a long delay before an error message is returned.
In a complex application, this situation can tie up enough resources on the web server that other unrelated functions begin to exhibit problems as well.
Therefore, it would be desirable to have a means of dealing with-situations in which the performance of an application is degraded due to any reasons, such as the ones discussed above.